Drinking: Bridgeport in NW Portland but my fav place is the Lucky Lab on Hawthorne.
Eating: The food carts are great.
Touristy stuff: Cable car up to OHSU, Rose gardens, Japanese gardens, Portland Zoo, Voodoo donuts.
Shopping/people watching : SE Hawthorne.
Community events/people watching: Last Thursday in NW Alberta.
Biking: Rent a bike and ride from Waterfront Park downtown to the Sellwood Bridge and cross the Willamette River and ride back along the railroad bike path to OMSI and cross back into town on the Hawthorne Bridge (about 10 miles - some construction towards and on the Sell wood Bridge)
Sports: Watch a Timbers game at Jeld Wen Park.
Outside the city: Columbia River Gorge and waterfalls, Trillium Lake for views of Mt Hood.
The Japanese garden at Washington Park above downtown will be photo friendly regardless of weather in late October (which well may be still good), and the views from the Rose Garden there or from the Pittock Mansion nearby may present good vistas depending on weather, and the classical Japanese garden downtown is worth a visit.
Second the Multnomah Falls suggestion, and add Crown Point along the way for some Columbia River Gorge views (again, weather-dependent) without having to leave the greater Portland area
If you have the chance, try to eat at Ox restaurant, (Argentine-style grilled meats) or Toro Bravo (inventive tapas style) - both are on the inner east side of the river, still close to downtown. Gruner is good and downtown; Ataula on/near NW 23 and Thurman is Basque tapas.
If you enjoy good beer, there are three or four small quality breweries in lower SE/NE - Upright Brewing, Burnside Brewing, Cascade Brewing (sour beers), and Commons.
Wine bar- try Noble Rot, great wine list, on the rooftop with view of downtown from lower east side - on Burnside.
Upscale cocktails with views - try The Nines Hotel bar called Departures on the top floor downtown on Morrison St, open patios weather permitting, or Portland City Grill on @37th floor of the Big Pink tower on downtown Burnside; for a good non-view bar try Teardrop in the Pearl/NW, the Park Kitchen on the park blocks downtown, or the Doug Fir on east Burnside.
The art museum on the downtown park blocks will have a show of samurai armor ongoing then if you are into that type of thing